GIFT  OF 

^r  .n.L.LeuDP 


ENGINEER  DEPARTMENT,  UNITED  STATES  ARMY. 


THE    ELEV^ATION 


SITES  FOE  SEACOAST  BATTERIES, 


JOHN    G^.    D.   KNIGHIT, 


MAJOR,  CORPS   or  ENOINKERS,  U.  8.  A. 


WASHINGTON; 

GOVERNMENT  PRINTING  OFFICE. 

1896. 


ENGINEER  DEPARTMENT,  UNITED  STATES  ARMY. 


THE    ELEVATION 


OF 


SITES  FOR  SEACOAST  BATTERIES, 


JOHN    G^.    D.   KNIG^HT, 

MA.IOll,  COUPS   OF   EN(iINF.Et{S,  U.  8.  A. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1896. 


WAR  DEPARTMENT 

DocTunent  No.  98." 

Office  of  the  Chief  of  Engineers. 


t 


Office  of  the  Chief  of  Engineers, 
United  States  Army, 

Washington,  D.  C,  July  9,  1896. 

Sir:  I  have  the  honor  to  submit  herewith  a  paper  prepared  by  Maj.  John  G.  D.  Knight, 
Corps  of  Engineers,  on  the  influence  of  the  command  of  a  battery  on  its  efficiency. 

This  paper  contains  information  of  great  value  to  officers  of  the  Corps  of  Engineers 
concerning  the  elevation  of  sites  for  seacoast  batteries,  and  I  recommend  that  authority  be 
granted  to  have  it  printed  at  the  Government  Printing  Office,  and  that  two  hundred  copies 
be  obtained  for  the  use  of  the  Engineer  Department  upon  the  usual  requisition. 
Very  respectfully,  your  obedient  servant, 

W.  P.  Craighill, 
Brig.  Gen.,  Chief  of  Engineers. 
Hon.  Daniel  S.  Lamont, 

Secretary  of  War. 


[1st  Indorsement.] 


War  Department, 

July  17,  1896. 
The  recommendation  of  the  Chief  of  Engineers  is  approved. 
By  order  of  the  Secretary  of  War : 

John  Tweedale, 

Chief  Clerk. 


(8) 


667362 


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WiLLETs  Point,  N.  Y., 

April  7,  1896. 

Colonel : 

The  Board  of  Engineers  having  now  under  consideration  tlie  subject  of  the  elevation  of 
sites  for  batteries,  and  having  requested  me  to  elaborate  views  expressed  by  me  on  that  sub- 
ject, I  have  the  honor  to  submit  the  following : 

What  should  be  the  proper  elevation  of  a  seacoast  battery  can  not  be  determined  with- 
out considering  the  fire  to  which  it  will  be  exposed  and  that  which  it  may  return;  not  the 
weight  of  projectiles,  but  more  especially  the  angles  at  which  they  will  arrive  at  their  tar- 
gets and  certain  functions  of  those  angles. 

I.  This  requires  at  once  some  assumption  as  to  the  ranges  at  which  batteries  may 
expect  to  be  attacked. 

During  the  English  naval  maneuvers  of  1890,  the  first  rule  for  engaging  was  "Fire  is 
not  to  be  opened  or  continued  at  a  greater  distance  than  4,000  yards." 

During  those  of  1893,  when  the  fleets  went  into  action,  "the  leaders  were  then  passing 
in  opposite  courses,  x>ort  to  port,  distant  about  a  mile,  fire  from  main  and  secondary  guns 
being  opened  as  each  vessel  came  into  range  of  an  o])ponent."  Later  they  engaged  when 
about  f  mile  distant. 

In  the  French  maneuvers  of  1893,  "ships  were  always  to  be  considered  as  in  action 
when  they  were  within  3,280  yards  of  one  another."  At  the  close  of  these  maneuvers  three 
vessels,  steaming  at  10  knots,  fired  at  the  summit  of  Cape  Rosso,  distant  8,750  yards,  with 
14  and  16  centimeter  guns;  and  six  battle  ships,  steaming  at  8  knots,  fired  at  a  range  of 
3,800  yards  with  all  their  guns.  Finally  the  first  three  fired  at  a  target  8,750  yards  distant, 
while  steaming  at  10  knots,  in  the  arc  of  a  circle  of  which  the  target  was  the  center.  "The 
results  are  said  to  have  been  only  moderately  satisfactory." 

In  the  English  maneuvers  of  1894,  it  was  ruled  that  an  enemy's  ship  coming  within 
(j,000  yards  of  the  entrance  to  a  fortified  port  was  to  be  out  of  action  for  twenty-four  hours. 
One  engagement  began  at  4,000  yards  range. 

The  distances  at  which  the  forts  of  Alexandria  were  attacked  by  the  English  fleet  varied 
at  first  from  1,000  to  3,800  yards. 

At  Sfax  the  French  ironclads  were  stationed  at  from  7,000  to  4,300  yards,  boats  being 
at  "a  few  hundred  yards."  "After  a  remarkably  deliberate  fire  of  2,000  projectiles, 
delivered  under  peace-practice  conditions,  the  '  defensive  power '  of  the  place  is  reported 
to  have  been  'practically  uninjured.'  " 

Sir  Andrew  Clarke,  Inspector  General  of  Fortifications,  in  this  connection  stated :  "It 
will  need  a  great  deal  of  shooting  from  the  gun  vessels  before  a  shore  gun  is  grazed,  and  the 
ironclads  will  do  no  harm  at  all  to  the  defenses." 

In  the  battle  of  The  Yalu,  September  17,  1894,  the  Chinese  opened  fire  at  a  distance  of 
from  5,500  to  6,500  yards;  the  Japanese  replied  at  3,300  yards.  The  battle  was  fought  in 
general  at  ranges  of  from  2,000  to  3,300  yards. 

(5) 


6 

The  cases  above  cited  lead  to  tlie  conclusion  tliat  it  is  not  probable  that  a  naval  attack 
of  land  batteries  will  be  entered  upon  at  distances  exceeding  5,000  yards. 

It  is  not  asserted  that  cities,  dockyards,  and  large  harbors  densely  occupied,  may  not  be 
bombarded  from  distances  exceeding  5,000  yards;  but  the  probable  damage  to  batteries  from 
attack  at  the  same  distances  will  not  justify  the  expenditure  of  ammunition. 

II.  From  the  ballistic  curves  computed  under  the  direction  of  the  Board  of  Engineers 
in  1885  for  the  40-centimeter  Krupp  breecli-loading  rifle,  and  in  1892  for  the  United  States 
8  and  10  inch  breech-loading  rifles,  the  following  table  has  been  prepared: 


Angles  op  fall. 


Range. 


8-inch  gun.    I  lo-inch  gnn.      4(H;m.  gun; 


1,000  yards - 
2, 000  yards- 
3,000  yards. 
4, 000  yards. 
5, 000  yards. 


DegreeK. 

0.7 
1.5 
2.6 
3.9 
5.7 


Degrees. 

0.8 
1.8 
3.0 
4.4 
6.1 


Degrees. 

0.6 

1.6 
2.5 
3.7 
4.9 


Initial  velocity  per  second 


Fea. 

2,160 


Feet. 
1,960 


2,035 


It  is  assumed  that  batteries  will  not  be  the  targets  for  projectiles  having  greater  angles 
of  fall  than  those  given  for  the  10-inch  rifle.  Should  vessels  be  armed  with  guns  mounted 
for  curved  fire,  overhead  protection  may  be  required  for  land  guns,  since  increased  elevation 
of  site  will  in  itself  give  no  increased  protection  against  such  fire. 

In  batteries  where  the  guns  are  mounted  on  Buffington-Crozier  carriages  and  are  not  to 
be  fired  at  angles  of  depression,  the  gun  after  recoil  lies  wholly  below  a  plane  which  passes 
through  the  interior  crest  and  is  depressed  7  degrees  below  a  horizontal  plane.  In  other 
words,  the  gun  after  recoil,  could  not  be  hit  by  projectiles  clearing  the  interior  crest  and  hav- 
ing angles  of  fall  of  less  than  7  degrees.  Briefly,  the  gun  may  be  said  to  be  under  a  7-degree 
plane.  This  plane  passes  5  feet  11  inches  above  the  front  edge  of  the  loading  platform  and 
4  feet  4  inches  above  the  extreme  rear  edge. 

When  a  10-inch  rifle  is  mounted  on  a  Gordon  carriage,  it  is  under  a  13-degree  plane  after 
recoil  and  while  being  loaded  at  an  elevation,  and  under  a  10-degree  plane  while  being 
loaded  in  a  horizontal  position.  This  10-degree  plane  passes  5  feet  10  inches  above  the  front 
edge  of  the  loading  platform  and  4  feet  3  inches  above  the  extreme  rear  edge. 

The  12-inch  rifle  mounted  on  the  lift,  when  the  lift  is  completely  lowered,  lies  under  a 
15.5-degree  plane,  and  the  rear  upper  edge  of  the  pit  lies  under  a  9-degree  plane.  The  15.5- 
degree  plane  passes  about  8  feet  above  the  floor  of  the  loading  passage  at  the  ammunition 
hoist. 

The  greatest  angle  of  fall  of  projectiles  for  a  range  of  5,000  yards  given  in  the  table 
above  is  6.1  degrees;  hence  neither  guns  mounted  on  the  types  of  carriages  mentioned  or  on 
lifts,  nor  the  carriages  or  lifts,  will  be  struck  by  projectiles  passing  above  interior  crests 
where  ranges  are  5,000  yards  and  less,  and  the  fire  is  direct,  even  though  the  crest  of  the  land 
battery  is  at  the  level  of  the  attacking  naval  battery. 


As  these  shot  will  pass  at  least  5  feet  G  inches  above  the  rear  edge  of  the  loading  plat- 
form of  the  10-inch  Buffington-Crozier  carriage  and  about  7  feet  above  the  front  edge,  the 
gun  detachment  will  be  fairly  covered  from  them.  Where  guns  are  mounted  en  barbette  on 
nondisappearing  carriages,  both  gun  and  loading  detachment  are  almost  wholly  above  the 
level  of  the  interior  crest.  In  one  case  where  a  12-inch  gun  has  been  so  mounted,  the  load- 
ing platform  is  about  3  inches  above  the  level  of  the  interior  crest. 

III.  To  what  extent  will  the  protection  of  guns  and  gun  detachments  be  increased  by 
selecting  elevated  sites  for  batteries  ? 

The  following  table  shows  the  heights  at  different  ranges,  giving  corresponding  reduc- 
tions of  the  angles  of  fall  of  arriving  projectiles,  with  corresponding  theoretical  vertical 
increase  of  protection  of  loading  detachment,  45  feet  in  rear  of  crest ;  this  distance  being 
approximately  the  distance  of  the  rear  edge  of  the  loading  platform  from  the  interior  crest : 


Angle  of  fall  diminislx'd — 


1  degree  _ 

2  degrees 

3  degrees 

4  degrees 

5  degrees 


Tlieoretical 

vertical 

increase  of 

protection 

45  feet  from 

crest. 

1,000  yds. 

Incite'. 

Feet. 

9 

52 

19 

105 

38 

157 

38 

210 

47 

262 

El.BVATlON    ABOVE   NAVAL  0CN8  AT- 


2,000  yds.       3,000  yds.       4,000  yds.       5,000  yds, 


Veel. 
105 

210 
314 
420 
525 


Feel. 

Feel. 

157 

209 

314 

419 

472 

629 

639 

839 

787 

1,050 

Feet. 

263 

524 

786 

1,049 

1,312 


It  is  apparent  at  once  that  against  fire  from  vessels  a  mile  or  more  distant,  no  moderate 
increase  in  the  elevation  of  the  site  of  a  battery  will  give  much  increase  in  protection.  But 
such  slight  protection  of  loading  detachment  as  is  given  is  largely  theoretical,  for  elevations 
corresponding  to  the  greater  reductions  in  the  angle  of  fall.  When  this  angle  of  dejjression 
is  5  degrees,  the  platform  of  the  8-inch  gun  is  11  inches  higher  relative  to  the  interior  crest 
than  when  the  gun  is  to  be  fired  without  depression;  and  that  of  the  10-inch  gun  12.5  inches; 
the  net  increase  of  protection  of  loading  detachment  due  to  elevation  of  site  in  these  cases  is 
30  and  35  inches,  respectively.  This  is  the  increased  protection  afforded  at  a  distance  of  45 
feet  in  rear  of  the  crest  202  feet  above  the  guns  of  a  vessel  1,000  yards  distant.  If  the  range 
be  doubled  or  trebled,  the  crest  elevation  must  also  be  doubled  or  trebled,  not  to  obtain  more 
than  3G  inches  additional  protection,  but  to  retain  that  increase.  The  explanation  of  this  is 
that  each  increase  in  the  elevation  of  the  site  requires  the  loading  platform  to  be  raised  nearer 
the  level  of  the  interior  crest  in  order  that  the  land  gun  may  be  fired  at  increased  angles  of 
depression.  Otherwise  dead  angles  would  be  developed  in  front  of  a  battery  in  proportion 
to  the  increase  in  the  elevation  of  its  site. 

The  second  table  gives  what  may  be  called  the  searching  effect  of  projectiles  and  the 
elevation  of  site  that  will  neutralize  this  effect.  Thus  a  projectile  having  an  angle  of  fall  of 
1  degree  just  clearing  the  interior  crest  will,  at  a  distance  of  45  feet  to  the  rear,  pass  0  inches 
below  the  crest.     This  is  the  angle  of  fall  of  projectiles  fired  at  a  range  of  about  1,000  yards. 

What  elevation  of  the  battery  site  will  neutralize  this  angle  of  fall,  or  cause  the  path  of 
the  projectiles  on  arrival  to  be  horizontal '? 

The  table  shows  that  an  elevation  of  52  feet  is  necessary. 


8 

For  ranges  of  about  2,000  yards  the  angle  of  fall  will  be  about  2  degrees,  and  the  project- 
ile will  pass  19  inches  below  the  crest.  To  neutralize  this  fall,  the  elevation  of  the  site  must 
now  be  210  feet,  and  so  on,  until  a  projectile  fired  at  a  distance  of  between  4,000  and 
5,000  yards  having  an  angle  of  fall  of  about  5  degrees  will  pass  47  inches  below  the  interior 
crest.     To  neutralize  this  the  site  must  have  an  elevation  of  over  1,000  feet. 

IV.  To  what  extent  will  the  field  of  fire  of  the  battery  be  restricted  by  elevating  its  site  ? 
These  different  elevations  have  reduced  the  angles  of  fall  of  arriving  projectiles  to  0, 

and  have  thus  neutralized  their  searching  power. 

But  what  has  been  the  efl^ect  upon  the  land  guns,  of  thus  elevating  the  battery  site  ? 

These  guns  are  mounted  on  carriages  allowing  the  guns  but  5  degrees  depression ;  hence 
they  can  not  be  used  against  vessels  at  ranges  requiring  them  to  be  depressed  more  than  5 
degrees. 

A  10-inch  rifle,  firing  over  a  crest  .300  feet  above  the  water,  will  have  a  dead  zone  whose 
radius  is  about  1,000  yards;  one  firing  over  a  crest  whose  elevation  is  210  feet  will  have  a 
dead  zone  of  about  720  yards  radius. 

V.  It  has  been  shown  that  a  gun  mounted  on  either  of  three  disappearing  plans  will  not 
be  directly  hit  when  under  direct  fire  of  guns  at  ranges  not  exceeding  5,000  yards;  that  the 
additional  protection  arising  from  the  tabulated  elevations  of  site  is  both  unnecessary  and 
slight  for  guns  thus  mounted,  and  is  practically  nothing  for  nondisappearing  barbette  guns ; 
and  that  moderate  elevations  of  site  result  in  dead  zones,  which  should  not  be  disregarded. 
Still  there  seems  one  reason  why  sites  should  be  chosen  having  more  elevation  than  that  of 
naval  guns.  With  nothing  but  the  parapet  continuously  in  an  enemy's  view,  with  guns 
appearing  only  for  brief  periods,  he  must  be  at  a  loss  how  to  direct  his  fire  if  he  can  not  see 
the  openings  into  which  the  gun  disappears.  Therefore,  with  the  object  of  depriving  an 
enemy  of  a  definite  target  for  his  guns,  the  battery  may  well  be  constructed  at  sufficient 
elevation  to  hide  the  openings  of  its  emplacements  from  view  from  the  tops  of  an  enemy's 
vessel.  For  this  purpose,  and  for  this  only,  it  may  be  well  to  give  crests  of  batteries  an 
elevation  of  about  100  feet  above  the  water. 

As  the  loading  platforms  of  barbette  guns  on  nondisappearing  carriages  are  about  on 
the  level  of  the  interior  crest,  even  when  the  site  of  the  battery  is  about  300  feet  high,  it  is 
evident  from  the  table  given  that  the  service  of  these  guns  without  shields  demands  much 
exposure  of  gunners,  no  matter  what  reasonable  elevation  the  battery  may  have. 

VI.  So  far  shell  and  shrapnel  have  not  been  considered.  With  even  the  low  remaining 
velocity  of  1,200  feet,  but  0.04  second  would  be  required  for  a  shell  to  pass  from  the 
interior  crest  to  the  rear  of  the  emplacement.  It  is  hardly  too  much  to  say  that  the  time 
fuze  could  not  be  cut  with  the  accuracy  necessary  to  insure  the  burst  of  the  shell  at  some 
point  of  its  passage  over  the  gun  and  its  gunners.  At  the  Inchkeith  experiments,  in  1884, 
firing  was  carried  on  against  a  model  gun  emplacement  and  dummy  gunners.  Thirty  rounds 
of  shrapnel,  fired  from  a  10-inch  gun  at  an  excellent  target  and  under  exceptionally  favorable 
circumstances,  resulted  in  four  of  the  dummies  being  hit ;  the  target  gun  was  still  perfectly 
capable  of  being  worked.  Some  years  ago  French  vessels  did  not  carry  shrapnel  for  heavy 
guns. 

If  direct  hits  can  be  guarded  against,  and  thus  the  action  of  percussion  fuzes  prevented, 
shell  and  shrapnel  need  not  be  feared  where  guns  are  mounted  on  disappearing  devices. 

VII.  Certain  advantages  have  been  attributed  to  low  sites. 

(a)  "They  afford  no  direct  fire  upon  the  deck  of  a  ship,  which,  being  her  most  vulner- 
able point,  should  always  be  attacked." 


9 

For  equal  ranges  the  angles  of  fall  for  tlie  land  guns  would  be  increased  only  as  little  as 
those  of  the  naval  guns  would  be  decreased  for  corresponding  elevations  of  site. 

Lieut.  E.  W.  Very,  U.  S.  N.,  asserts  that  2-inch  steel  plates  well  supported  against  flexure, 
will  give  good  resistance  at  angles  up  to  9  degrees  and  possibly  10  degrees.  The  angles  of 
fall  of  heavy  projectiles  for  ranges  up  to  3,000  yards  do  not  exceed  3  degrees.  Were  the 
elevation  of  the  battery  site  increased  to  such  an  extent  as  to  increase  these  angles  of  fall  by 
5  degrees,  a  well-supported,  flat  2-inch  steel  deck  would  still  give  good  resistance  at  these 
ranges.  The  second  table  given  above  shows  how  great  are  the  elevations  necessary  to  give 
this  increase  to  angles  of  fall,  an  increase  still  insufficient  to  cause  the  deck  to  be  penetrated. 
A  slight  roll  of  the  vessel  may  offset  the  small  change  in  the  angle  of  fall  due  to  increased 
elevation  of  battery  site ;  on  the  other  hand,  such  a  roll  may  unfavorably  expose  the  deck  to 
shot  from  a  low  battery. 

(6)  A  low  site  "enables  ships  to  dispense  with  high  angles  of  fire,  for  which  the  mode 
of  mounting  their  guns,  in  a  measure,  disqualifies  them." 

For  neither  of  the  United  States  guns  above  mentioned  do  the  angles  of  elevation  corre- 
sponding to  ranges  of  5,000  yards  exceed  5  degrees.  For  the  ranges  and  elevations  of  site 
above  tabulated,  additional  elevations  of  the  naval  guns  do  not  exceed  5  degrees. 

The  maximum  elevation  of  the  piece  then  for  attacking  batteries  with  the  elevations  of 
site  and  ranges  given,  will  be  under  10  degrees. 

The  maximum  practicable  elevation  for  guns  on  shipl)oard  being  from  13  to  15  degrees, 
it  appears  that  the  attack  of  ])atteries  on  sites  of  the  elevations  given  above  does  not  demand 
impracticable  angles  of  fire  for  naval  guns  at  reasonable  ranges. 

(c)  ' '  It  places  the  hostile  guns  on  shipboard  on  an  equality  with  land  guns  as  to  energy 
of  impact."  As  an  illustration,  attention  is  called  in  the  text  from  which  this  is  quoted  to 
the  16-inch  rifle  firing  a  1-ton  projectile  from  a  bluft'  200  feet  high  and  a  ship  firing  j)roject- 
iles  of  like  weight  at  the  battery ;  the  ship  being  thus  handicapped  400  foot-tons.  Still  the 
land  gun  has  gained  only  200  foot-tons  by  the  elevation  of  the  battery  site,  or  about  one-half 
of  1  per  cent  of  its  striking  energy  at  a  range  of  2  miles. 

If  a  714-pound  shot  be  fired  from  a  ship  at  3,000  yards  range  at  a  battery  elevated  1,270 
feet,  and  another  shot  of  the  same  weight  fired  from  the  battery  at  the  ship,  the  respective 
striking  velocities  would  be  1,474  and  1,517  feet  per  second,  and  the  respective  striking 
energies  10,754  and  11,390  foot-tons;  the  vessel  in  this  case  would  be  handicapped  636  foot- 
tons. 

But  the  gun  has  only  gained  3  per  cent  of  energy  by  reason  of  its  elevated  emplacernent. 

If  a  blow  of  11,100  foot-tons  would  not  damage  a  steel  deck,  would  one  of  11,400  be 
likely  to  do  so  ? 

The  authority  urging  the  above  objections  concludes  the  subject  with  this  statement : 
"Even  at  Fort  Mex,  a  low  work  at  Alexandria,  out  of  920  shots  fired  at  14  guns  practically 
en  barbette  by  five  armored  ships  at  ranges  from  1,000  to  3,800  yards,  two  land  guns  were 
grazed  but  none  were  disabled  by  direct  hits ;  and  only  direct  hits  can  place  a  gun,  properly 
mounted  on  a  bluff,  liors  de  combat.''^ 

So  far  as  this  action  throws  light  on  this  subject,  the  only  disadvantage  entailed  upon 
Fort  Mex  by  its  crest  being  less  than  30  feet  above  sea  level  was,  that  two  guns  out  of 
fourteen  were  grazed ;  even  though  low,  its  guns  escaped  direct  hits. 

2087 2 


10 


CONCLUSION. 


Assuming  that  vessels  \Nill  not  attack  batteries  at  greater  ranges  than  5,000  yards, 
barbette  guns,  mounted  according  to  any  of  the  disappearing  methods  adopted  by  the  United 
States,  need  no  additional  protection  derived  from  increasing  the  elevation  of  battery  sites 
•within  reasonable  limits.  Even  moderate  elevations  of  batteries,  which  are  armed  with 
guns  limited  to  depression  of  5  degrees,  entail  dead  zones  of  magnitude  not  to  be  overlooked 
where  these  zones  include  areas  of  deep  water. 

Disappearing  guns  gain  but  little  additional  protection  by  such  increase  in  the  battery 
elevation,  and  nondisappearing  guns  gain  therefrom  practically  no  additional  protection. 

Therefore,  unless  justified  by  motives  of  economy,  barbette  guns  should  not  be  mounted 
on  nondisappearing  carriages  even  on  elevated  sites.  The  special  advantage  of  elevated 
sites  for  batteries  of  disappearing  guns  is,  that  they  put  obstacles  in  the  way  of  an  enemy 
seeking  to  locate  the  guns.  This  advantage  will  be  secured  if  the  battery  crest  have  an 
elevation  of  about  100  feet. 

Very  respectfully, 

John  G.  D.  Knight, 

Major,  Corps  of  Engineers. 

Col.  H.  M.  Robert, 

Corps  of  Engineers,  U.  S.  Army, 
President  Board  of  Engineers, 

New  York  City. 


e673f.2 


L)F4-s- 


UNIVERSITY  OF  CALIFORNIA  UBRARY 


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